Explosively actuated rivet gun

ABSTRACT

A BARREL ASSEMBLY OF AN EXPLOSIVELY ACTUATED RIVET GUN INCLUDES A BARREL HOUSING AND AN INNER, LONGITUDINALLY DISPLACEABLE BARREL WITHIN THE HOUSING. A TRANSLATABLE IMPACTING HAMMER IS DISPOSED WITHIN THE INNER BARREL FOR STRIKING A RIVET FORMING PUNCH AT THE MUZZLE END OF THE GUN. PORTING IN THE INNER BARREL PROVIDES FOR ITS MOVEMENT IN RESPONSE TO GAS PRESSURE TOWARD THE BREECH END OF THE GUN AND THE VENTING OF EXPOSIVE GENERATED GASES. AN IMPACTING HAMMER RETURNPORT IN THE INNER BARREL ADMITS GASES AHEAD OF THE IMPACTING HAMMER TO FORCE IT BACK TO THE BREECH END OF THE GUN. THE PORTING ALSO PRODUCES GAS BIASING OF A NOSE ASSEMBLY AGAINST THE SHEETS BEING RIVETED TO ELIMINATED THE EFFECT OF GUN RECOIL. THE IMPACTING HAMMER, THROUGH INERTIA SEPARATION, PROLONGS THE TRANSFER OF ITS UPSETTING IMPACT TO A RIVET. THE FORMING PUNCH HAS A FRUSTO-CONICAL RECESS FOR UPSETTING AND CONSTRICTING EXPANSION OF A RIVET. THE NOSE ASSEMBLY HAS A UNIVERSALLY ROTATABLE HEAD WITH A PARABOLIC MIRROR THAT IS MAINTAINED OUT OF ALIGNMENT WITH A LIGHT SOURCE ON THE BREECH ASSEMBLY UNTIL THE NOSE ASSEMBLY IS PROPERLY ALIGNED, WHEREUPON LIGHT REFLECTED FROM THE PARABOLIC MIRROR ENERGIES A PHOTOSENSITIVE ELEMENT TO UNLOCK THE GUN&#39;&#39;S TRIGGER. ADDITIONAL INTERLOCKS PREVENT GUN FIRING UNTIL A RIVET BUCKING BAR AND A FORMING DIE ARE IN PROPER POSITION. AN ADJUSTABLE VOLUME EXPANSION CHAMBER CONTROLS EXPLOSIVE PRESSURE ON THE IMPACTING HAMMER AND, THEREFORE, THE UPSETTING IMPACT TRANSFERRED THROUGH THE FORMING PUNCH TO A RIVET.

Feb. 2, 1971l J. c. sTElNME-rz 3,559,449

ExPLosIvELY ACTUATED RIVET GUN Filed Nov. 19, 196e l s sheets-sheet 2vZ22* g fw pff /X/x//m/ m ///wlf////S Feb, 2, 1971 y J. c. STEINMETZ IEXPLOSIVELY ACTUATED RIVET GUN Filed Nov. 19, 1968 3 Sheets-Sheet 5Arme/ufr;

U.S. Cl. 72-430 51 Claims ABSTRACT F THE DISCLOSURE A barrel assembly ofan explosively actuated rivet gun includes a barrel housing and aninner, longitudinally displaceable barrel within the housing. Atranslatable impacting hammer is disposed within the inner barrel forstriking a rivet forming punch at the muzzle end of the gun. Porting inthe inner barrel provides for its movement in response to gas pressuretoward the breech end of the gun and the venting of exposive generatedgases. An impacting hammer return port in the inner barrel admits gasesahead of the impacting hammer to force it back to the breech end of thegun. The porting also produces gas biasing of a nose assembly againstthe sheets being riveted to eliminated the effect of gun recoil. Theimpacting hammer, through inertia separation, prolongs the transfer ofits upsetting impact to a rivet. The forming punch has a frusto-conicalrecess for upsetting and constricting expansion of a rivet. The noseassembly has a universally rotatable head with a parabolic mirror thatis maintained out of alignment with a light source on the breechassembly until the nose assembly is properly aligned, whereupon lightreflected from the parabolic mirror energies a photosensitive element tounlock the guns trigger. Additional interlocks prevent gun firing untila-rivet bucking bar and a forming die are in proper position. Anadjustable volume expansion chamber controls explosive pressure on theimpacting hammer and, therefore, the upsetting impact transferredthrough the forming punch to a rivet.

The present invention relates to an explosively actuated tool forsetting rivets which is particularly useful for setting rivetsfabricated from hard material.

The effectiveness of a riveted joint is dependent on the shear strengthof the rivet. With high shear strength rivets, smaller holes in thefastened sheets may be used while maintaining the riveted jointsintegrity. The overall effect of high strength rivets results inlightweight riveted structures. Additionally, the use of high strengthrivets results in substantially improved joint fatigue life. Therefore,rivets fabricated from such high strength materials as titanium or steelalloys are highly desirable in weight critical structures such as foundin aircraft.

An effective riveted joint also requires that the set rivet itself havesubstantial fatigue resistance. Hard materials such as titanium andcertain steel alloys, however, are brittle and extremely difficult toupset without creating fatigue life limiting structural tiaws. As aconsequence of these characteristics, la rivet head formed by a sharp,distinct blow of suflicient magnitude to upset the hard material of therivet has heretofore produced cracking and lines of weakness in theformed head and proximate shank portions. Riveted joints employing hardrivets set by uncontrolled impact also tend to unevenly deform the sheetthrough which the rivet extends, as the sheet tends to expand to agreater extent adjacent where the rivet end is upset. This uneven sheetexpansion reduces joint fatigue life by overexpansion near the formedhead and insutlicient expansion of hole walls in the balance of thejoint.

Because of the ditliculties encountered with hard rivet United StatesPatent O materials in producing an effective riveted joint, prior artdevelopments have been directed to high pressure, squeeze setting ofhard rivets. This high pressure, squeeze setting slowly applies asetting force on both ends of the rivet. While effective, this method ofriveting has limited application. The equipment necessary to apply theextremely large compressive forces through both ends of a rivet must, ofnecessity, be large and expensive because the equipment must span largedistances in reaching interior areas Vto be riveted. These largedistances require the equipment to be extremely large to have thestrength required to withstand the large flexure loads produced by thesetting force. Moreover, the equipment is only useful, because of itssize, for riveting large, relatively llat subsections which aresusceptible to fabrication away from the final assembly of which theyform a part. In aircraft air frame fabrication, for example, theproduction of subassemblies of this type is possible for only a smallproportion of the total air frame.

Therefore, there is a demand for a hand or portable tool which caneiectively produce a high strength riveted joint employing rivetsfabricated from hard materials. Such a tool cannot employ the squeezetechnique because of the weight and size of the tool required to applythe necessary compressive force and the requirement for applying such aforce on either end of the rivet well within the panels being riveted.

The present invention provides an explosively actuated impact toollwhich may be used to set a wide variety of rivets. In its preferredform, the present invention provides an explosively actuated impact toolwhich is capable of upsetting rivets fabricated from hard materials,such as titanium or certain steel alloys, to produce an eifectivelyriveted joint.

In one form, the present invention contemplates an explosively actuatedtool or gun for setting rivets which maintains a nose of the gun rmlyagainst the structure being riveted during the upsettingof a rivet,notwithstanding the tendency of the gun to recoil. The gun includes abarrel having a bore for receiving an impacting hammer disposed fortranslation from the breech end of the barrel toward the barrels muzzleend in response to the -ring of an explosive charge. A forming punch orhammer at the muzzle end of the gun is disposed to be struck by theimpacting hammer, translate in a bore of the nose and impart anupsetting force to a rivet. Means is provided for receiving an explosivecharge at the breech end of the barrel such as a breech plug disposed ina breech block. Means is also provided for selectively firing anexplosive charge disposed in the explosive charge receiving means. Thenose is mounted at the muzzle end of the barrel for abutting against thesurface of the structural sheet surorunding the rivet to be formed. Thenose is coupled to the barrel such that gas generated by the detonationof an explosive charge biases or urges the nose against the sheets Whileallowing the barrel to recoil.

In one embodiment of the present invention, the forming punch has afrusto-conical recess and the nose has an annular constricting flangedisposed on the sheet side of the forming Ipunch. The frusto-conicalrecess of the forming punch acts on the end of a rivet to constrict itsradial expansion into the shape of the frusto-conical recess While theannular, inwardly directed constricting flange restrains the expansionof a collar-like forming die which may be employed with the rivet.

Means may also be `provided to prevent tiring of the explosive chargeand the consequent upsetting of a rivet unless the resulting impactforce is directed axially of the rivet. Such means may include auniversally rotatable or pivotable head, the Iposition of whichdetermines the position of the noses bore. The rotatable head may have asheet abutting surface and be mounted for limited rotation in a socket.The means may further include a. parabolic mirror, a light source, aphotosensitive element and a firing interlock. The parabolic mirror iscarried by the head to reflect light from the light source to thephotosensitive element when the gun is in proper alignment. Thephotosensitive element is in circuit with the firing interlock, whichmay be a solenoid on the path of the guns trigger, to prevent firinguntil the photosensitive element senses light reflected from theparabolic mirror. In order to prevent inadvertent firing, means may beprovided to positively maintain the parabolic mirror out of alignmentwith the photosensitive element until the gun is properly aligned withthe axis of the rivet to be set. Such means may include a spring mountedon a stationary portion of the nose and urging against the mirrorsmount. Alternately, the parabolic mirror may be maintained out ofalignment with the photosensitive cell by providing an inclined end atthe muzzle end of the inner barrel which normally maintains the mirrorout of alignment by bearing against a nose sleeve that carries therotatable or pivotable head. Additional interlocks which prevent gunfiring until -a forming die and a bucking bar are properly placed may beprovided.

It has been found, in upsetting rivets fabricated from hard materialswith an explosively actuated rivet setting gun or tool, that therequisite upsetting force required to upset the rivet must Ibe impartedto the rivet over a relatively prolonged period of time. `Statedalternately, the use of an impacting member which acts as a unitary masson the forming punch with sufficient force to upset the rivet with asingle blow produces cracking and oftentimes the disintegration of thehard rivet material being upset.

Accordingly, it is preferred in applications where the rivet gun is usedfor upsetting hard rivet materials to have the impacting hammer transferthe requisite upsetting force over a prolonged period of time relativeto the time, estimated as a part of a millisecond, that a unitary hammerof the same mass traveling at the same speed would act. This may beaccomplished by fabricating the impacting hammer from individualcylindrical segments which are held together through, for example, asplit pin disposed within the hammer along its longitudinal axis. Thisform of the impacting hammer apparently produces an inertial lag fromthe leading to the trailing segments as the impacting hammer isaccelerated by the explosive charge. On striking the forming punch, theleading segments are decelerated before the trailing segments to prolongthe period of impact.

An alternate form of an impacting hammer which prolongs the period ofimpact employs a heavy, fluid-like filler. This form of the impactinghammer has an axial cavity of progressively reduced cross section towardthe leading end of the impacting hammer. The interior of the cavity isfilled with a heavy fluid-like material, such as mercury, which lagsbecause of its inertia as the impacting hammer accelerates down thebarrel toward the forming punch. Upon striking the forming punch, thebody of the impacting hammer begins to decelerate rapidly while thefluid-like material moves rapidly toward the leading end of theimpacting hammer. As the fluid moves toward the leading end of theimpacting hammer, it encounters the areas of reduced cross section todecelerate and impart a delayed and prolonged impact force through thebody of the hammer to the forming punch.

An embodiment of the present invention employs means for varying theinitial expansion volume of the expanding gases produced by the ignitionof the explosive charge. This means allows for adjustment of theultimate impact force felt by the rivet and therefore admits to greaterflexibility of the gun. Such means may include a chamber having anadjustable sealing element disposed within it. 'Ille chamber is in gascommunication between the explosive charge and the impacting hammer withthe gases generated by the charge. The adjustment of the volume of thechamber adjusts the effective pressure acting against the muzzle end ofthe impacting hammer. Preferably, the seal element includes a dish orcup-shaped member which is capable of expanding radially against thewalls of the chamber to seal the chamber in response to the pressuregenerated by the explosive charge.

The rivet setting tool or gun of the present invention has a nose whichremains in abutting contact with the sheet or panel being rivetedbecause the nose is urged against the sheet by expanding, relativelyhigh pressure gases from the detonated explosive charge. Thisstabilizing facility of the gun avoids the adverse effects of recoilduring the setting of rivets.

The unique barrel construction of a preferred form of the presentinvention results in a very simple and economical gun. By the uniqueporting of the slidable barrel, spent gases produced by the explosivecharge are reliably vented to atmosphere when the barrel moves towardthe breech end of the gun. Moreover, the Iporting produces impact hammerreturn to its prefiring position by accelerating the hammer from themuzzle end of the barrel toward the breech end of the barrel after thesetting of a rivet.

In its preferred form, the rivet setting tool or gun of the presentinvention is particularly useful in setting rivets of very hardmaterial, such as rivets fabricated from titanium or steel alloy. Thetool is lightweight and portable and therefore may be readily used indifficult access areas or considerably inboard of large panel sections.By utilizing an explosive charge, sufficient force is available to upsetthe head of even the hardest rivets, thereby avoiding the use of squeezepressure setting of hard rivets. The frusto-conical recess of theimpacting hammer constrains the radial expansion of the rivet head beingformed in such a manner that unacceptable formed head cracking andweakening are avoided. With the frustoconical configuration, forexample, there is no tendency of the forming rivet head material toextrude into an annular space between an impacting member and astationary constraining sleeve or die which is a characteristic of atleast one prior art impact rivet gun presently known to the inventor andwhich, it is thought, leads to rivet failure. The unique construction ofthe impacting hammer to develop a sustained impact is also important inthe formation of a sound riveted joint with hard rivet materials.

Another advantage of an embodiment of the present invention resides inthe safety means for preventing the firing of the explosive charge whenthe barrel of the gun is not in proper alignment with the axis of therivet to be upset. The rotatably or pivotally mounted head of the gunreliably indicates alignment of the axis of the barrel and the axis ofthe rivet by enabling the parabolic mirror carried by the head toreflect light from the light source to the photosensitive element. Untilproper alignment, however, the photosensitive element cannot beenergized to release the locking means and `fire the explosive charge.The provision of firing interlocks which prevents gun firing until abucking bar and a forming die are properly positioned is alsosignificant in assuring proper rivet setting.

Another unique advantage of an embodiment of the present inventionresides in the facility for adjusting the expansion volume of the gasesgenerated by the explosive charge. This facility allows the velocity ofthe impacting hammer to be reduced 0r increased to adjust the formingforce imparted by the forming punch to the rivet. Variations in rivetmaterial characteristics and size may, therefore, be compensated for.

These and other aspects, features and advantages of the presentinvention will become more apparent from the following description,appended claims and drawings in which:

FIG. 1 is a foreshortened, side elevational view, partly in hal-fsection, of a preferred embodiment of the present invention;

FIG. 2 is a sectional view vtaken along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary sectional view taken along line 3 3 of FIG. 1;

FIG. 4 is a fragmentary sectional view taken along line 4-4 of FIG. 1;

FIG. 5 is a fragmentary half-sectional view of an alternate embodimentof the setting end of the gun of the present invention which illustratesthe position of a rivet to be set just prior to the impacting hammerstriking the depicted forming punch;

FIG. 6 is a half-sectional view similar to FIG. 5, illustrating theterminal stages of rivet upset produced with the rivet gun of thepresent invention;

FIG. 7 is a fragmentary view, partly in half section, of an alternateembodiment of the nose assembly of the present invention together with arivet to be set; and

FIG. 8 is a schematic circuit diagram of the various interlock or safetymeans of the present invention.

A preferred rivet setting gun or tool 10 of the present invention isillustrated in FIG. 1. In general, rivet gun 10 includes a barrelassembly 12 which slidably mounts a nose assembly 14. The barrelassembly is received on a breech assembly 16. A firing pin assembly 18in the breech assembly is capable of firing an explosive charge 20. Apistol grip firing assembly 22, including a trigger KJ and a hammer 26,is provided for actuating firing pin assembly 18 to detonate explosivecharge 20. An impacting hammer 28 is disposed within a bore 30 of aninner barrel 32 of the barrel assembly 12. The inner barrel is capableof limited longitudinal movement within the barrel assembly in responseto gas pressure. A forming punch or die 34 is normally disposed at themuzzle end of barrel assembly .12 within nose .assembly 14 for limitedtranslation. The impacting hammer is constructed to impart a sustainedimpact on forming punch 34 to prevent failure of riveted joints -whichis a particularly acute problem with hard rivet materials. In order tocontrol the velocity of impacting hammer 28 to that required for theproper upsetting of a rivet by forming punch or die 34, an expansionchamber assembly 36 is provided.

The improved rivet gun illustrated in FIG. 1 also has means forpreventing the guns firing until bore 30 of inner barrel 32 is properlyaligned. In general, these means include a parabolic mirror 38 mountedthrough a mirror mount or arm 40 on a ball-like, universally rotatableor pivotable head 42 of nose assembly 14, a light source 44, aphotosensitive element 46 and an interlock solenoid 48 in circuit withthe photosensitive element. A sheet abutting face or surface 50 of ballmember 42 and the noses bore 52 provide the means for accuratelyaligning the nose assembly. Light source 44 and photosensitive element46 are contained in a sighting bore 54 of a housing 56.

Before describing in further detail the construction of the preferredembodiments of the present invention, a brief description of operationwill be presented in order to facilitate the understanding of the moredetailed description which follows. In prering position, impactinghammer 28 resides at the breech end of bore 30 in inner barrel 32.Forming punch 34 receives the end of a rivet to be upset (as illustratedfor an alternate embodiment Expanding gases from the detonated charge 20act against the end of impacting hammer 28 to accelerate the impactinghammer toward the forming punch or die 34. The accelerating pressure iscontrolled by the volume in expansion chamber assembly 36. Gas actsagainst nose assembly 14 to maintain this assembly rmly against thesheets surrounding the extending end of the rivet. The hammer willcontinue on its course until striking forming punch or die 34 with asustained impact to upset a rivet in a manner illustrated in FIG.6.'Simultaneous with the forming operation, gas from the charge willbegin to act on impact hammer 28 to return the hammer to the breech endof the gun. Gas will also move barrel 32 toward the breech end of thegun to exhaust spent gases from bore 30 and the expansion volume ofexpansion chamber assembly 36.

With this brief description in mind, a more detailed description willnow be presented.

Barrel assembly 12 includes an outer barrel housing 58 disposedannularly around inner barrel 32. This housing has a first section 60and a second section 62. Section 60 is attached to section 62 at threads64. Section 60 is mounted to breech assembly 16 at threads 66. An innerbarrel return spring 68 is disposed about barrel 32 within section 6.2of housing 58. This spring urges against a shoulder 70 of section k60and an annular flange 72 which extends radially from barrel 32. Thespring urges inner barrel 32 toward the muzzle end of the gun. Anannular O-ring 74 is disposed in flange 72 to provide a seal againstleakage of explosive generated gases.

A longitudinal annulus 76 is present between housing section 62 and theoutside of barrel 32 toward the muzzle end of the barrel. Annulus 76 isin pressure and gas communication with bore 30 of barrel 32 through apair of pressurizing ports 78. A second longitudinal annulus is disposedbetween section 62 and the outside of barrel 32 at the extreme muzzleend of barrel 32. This longitudinal annulus is in pressure and gascommunication with the bore 30 of barrel 32 through pressurizing ports78 and a pair of impacting hammer return ports 82. Annulus -80 is incommunication with pressurizing ports 78 through annulus 76 and aplurality of passages 84 in an annular guiding flange 86 of barrel 32.These passages and guiding flange are best illustrated in FIG. 2. A pairof exhaust ports 87 at the breech out of barrel 32 provide for theexhausting of spent explosive charge generated gases as willsubsequently become more apparent. The inner diameter of housing section60 at the breech end of barrel 32 is reduced to provide a gas sealbetween this housing section and the barrel and prevent leakage throughexhaust ports 87.

Nose assembly 14 includes an annular mounting collar 88 which isdisposed for limited longitudinal translation on a reduced diametersection 90 of housing section 62. A radial, annular shoulder 92 ofmounting collar 88 is exposed to gas pressure within annulus 80 to urgethe nose assembly against a sheet of material being riveted. An O-ring94 in reduced diameter section 90 provides a gastight seal betweenmounting collar 88 and this section. A compression spring 96 is alsodisposed in annulus 80 to slightly bias nose assembly 14 longitudinallyaway from barrel assembly 1-2.

The nose assembly also includes ball member 42 as a universallyrotatable head. The ball member or head has a spherically curved surface98 which rotates in a spherical socket or seat 100 of mounting collar88. The extreme forward or muzzle end of mounting collar 88 is swedgedaround spherical surface 98 to retain ball member or head 42 in place.To allow a limited amount of rotational movement in aligning gun 10, anannular recess 102 is provided within ball member or head 42 to allowthe head to rotate with respect to the extreme muzzle end of barrel 32.An annular relief section 104 is also provided for head 42 to clear theextreme muzzle end of mounting collar 88. Sheet abutting face 50 of head42 is normal to bore 52 which extends through the longitudinal center ofthe head. An annular collar or constricting ange 106 extends radiallyinward to define the mouth of bore 52 and to constrict a forming collaror die employed with some hard rivets. An enlarged section 108 of bore52 extends longitudinally inward from constricting ilange 106 to mergeinto annular recess 102. This enlarged section 108 of bore 52 allows forlimited, captive longitudinal movement of forming punch 34 within head42. Mirror mount or support arm 40 extends upwardly from head 42 tosupport parabolic mirror 38, to be described in detail subsequently.

A spring 110 is disposed between mirror mount 40 and mounting collar 88to urge the parabolic mirror out of reflective alignment from photocell46 until sheet abutting face or surface 50 rests against a sheet.

Breech assembly 16 may take any number of forms. Briefly, however, theassembly illustrated includes a breech coupling member 112 which isthreadedly received on the male threads of housing section 60 of barrelassembly 12. A cylindrical, annular chamber 114 is disposed within thiscoupling member to allow for limited translation of barrel 32 and tocommunicate exhaust ports 87 with a pair of discharge ports 116 (shownin FIG. 3). Discharge ports 116 open into chamber 114 through the wallof coupling member 112. A threaded boss 118 extends from coupling member112 for receiving a cylindrical breech block 120. A breech plug 122 isdisposed within a bore in boss 1118. Breech plug 122 includes a head 124for abutting against a rearward, radial shoulder of boss 118. Beech plug122 also has a cylindrical counterbore 125 for receiving the rim ofcartridge 20. In the embodiment illustrated, explosive charge is in theform of a cased cartridge. However, it should be understood thatpellet-type charges may also be employed with the explosively actuated,rivet setting gun of the present invention. Breech plug 122 alsoincludes an annular groove 126 about its cylindrical periphery. Anexpansion port 128 opens into groove 126 for communication with thechamber of the expansion chamber assembly 36, to be subsequentlydescribed in detail. Breech plug 122 also has a cartridge receiving boreor chamber 130 which extends for the longitudinal length of the breechplug and opens into bore 30 of barrel 32 as well as into expansion port128. The muzzle end of breech plug 122 has an accurately machined,reduced diameter section 132 for telescopic, gastight receipt in bore 30of barrel 32.

Firing pin assembly 18 is received in breech block 120. Firing pinassembly 18 is maintained in its position illustrated by a compressorispring 134 which acts against an annular ange 136 of the assembly. Acylindrical extending portion 138 normally extends to the rear of breechblock 120. A firing pin 140 extends inwardly from inner cylindricalportion 142 of the firing pin assembly for striking the rim of cartridge20 in a standard manner. A bore 144 in breech block 120 admits tolimited longitudinal movement of the firing pin assembly to detonatecharge 20.

-Piston grip tiring assembly 22 is responsible for striking cylindricalextending portion 138 and thrusting firing pin 140 into the rim ofexplosive charge cartridge 20. This assembly includes a handle or gripbody 146 with a hammer 26 pivotally mounted through a pin 148 within arecessed portion 150 of handle 146. A cap 152 is attached on the face ofhammer 26 to strike cylindrical extending portion 138. A leaf spring 154extends from its mounting in a recess in the body of handle 146 to biashammer 26 in the direction of firing pin assembly 18. Trigger 24 ispivotally mounted to the body of handle 146 by a pin 156. A triggerreturn spring 158 biases trigger 24 into the position illustrated inFIG. 1. This spring abuts against a spring block 160 which is mounted tothe body of the handle portion. Hammer 26 is normally maintained in itscocked position by a sear 162 which is integrally formed will trigger24. This gear has a reduced transverse cross section as indicated mostclearly in FIG. 4. Hammer 26 has a recess 164 along one of its sides forreviewing sear 162 when trigger 24 is pulled. When trigger 24 is pulled,sear 162 rotates clockwise from its engagement with the body of hammer26 into recess 164. Hammer 26 will then rotate clockwise under theinfluence of spring 154 to strike cylindrical extending portion 138 offiring pin assembly 18 to extend firing pin 140 into the rim ofexplosive charge cartridge 20.

Impacting hammer 28 includes a plurality of cylindrical segments 166which are held together by a split retention pin 168 of standardconstruction. This retention pin is compressed when segments 166 areassembled over it to exert, through hoop stress, an outwardly directed,retention force on the walls of the axial bores of segments 166 to holdthe segments with the pin. The leading segment, indicated by referencenumeral 170, is of smaller diameter than the balance of the segments inorder to facilitate the admission of gas through impacting hammer returnports 82 to force the hammer to the breech end of barrel 32. Thetrailing segment of segments 166, indicated by reference numeral 172,mounts an expansion ring 173 which is in elastic contact with the wallof bore 30 of barrel 32. The frictional drag created by this expansionring is sufficient to retain impacting hammer 28 at the breech end ofbarrel 32 upon its return from the muzzle end of the barrel.

The segmented construction of impacting hammer 28 allows for a prolongedor sustained impact on forming punch 34 to spread the inertial effect ofthe impacting hammer over a period of time in excess of that which wouldbe presented by an impacting hammer of equal mass but of homogeneousconstruction. While the operation or elfect of the impacting hammer isnot completely understood, it is postulated that as the impact hammeraccelerates down the barrel toward the muuel end, small air gaps developbetween the segments because of inertial lag. Upon striking formingpunch or die 34, these air gaps tend to cause the segments to act asdiscrete masses. The resulting impact produces a large amount ofupsetting energy which is transferred through the forming punch or diewith sufficient force per unit of time to upset a rivet, but over a longenough period of time to prevent fracture or other structural defects inthe formed rivet.

FIG. 5 illustrates a suitable construction of forming punch or die 34.Forming punch or die 34 includes a frusto-conical recess 174 whichconverges inwardly of the face of punch 34, indicated by referencenumeral 175, toward the breech end of the tool. This recess includes aninwardly disposed impacting face 176 which is normal to the axis of theforming punch. The tapered flank or side of recess 174, indicated byreference numeral 178, serves to constrict the radial expansion of arivet while its end is being upset and to determine the nal shape of theformed rivet end. An enlarged cylindrical portion 180 of forming punch34 is slidably disposed in an enlarged section 182 of the nose sectionsaxial bore. Enlarged section 182 corresponds to enlarged section 108 ofnose assembly bore 52 of the embodiment illustrated in FIG. 1. Acylindrical driving portion 184 extends longitudinally toward the breechend of the barrel from enlarged cylindrical portion 180 and is slidablein bore 30 of barrel 32. An inwardly directed radial ilange 186 servesto constrict a rivet forming collar of the rivet being upset. This angecorresponds to flange 106 of the FIG. l embodiment. Because of the rapidchange in cross-sectional area between driving portion 184 and enlargedcylindrical portion 180, stress risers may occur in this transitionalzone of cross-sectional area which may cause failure of forming punch34. To prevent this eventuality, it is preferred that driving portion184 be separate from enlarged cylindrical portion 180. Alternately, theenlarged cylindrical portion may include the driving portion withoutreduction 9 in diameter between the two, as will be described withreference to FIG. 7.

In setting hard rivets, such as rivets may from titanium, forming punchor die 34 determines to a great extent the soundness of the resultingjoint.

Where weight is an important factor, the size of the upset end of rivetshould be as small as is possible to produce desired joint preload.Accordingly, the axial distance between face 175 and impacting face 176should be as small as is consonant with the development of a head thatwill withstand the tensile stress of preload. The depth of recess 174should also be relatively small if face 175 is not to strikeconstricting flange 186 and cause tool damage. (See FIG. 6 whichillustrates the desired spacing between face 175 and flange 1186 in thenally upset rivet head.)

The diameter of impacting face 176 is also important in producing anoptimum formed rivet head. This diameter should be slightly greater thanthe unformed diameter of the rivet to be formed. However, the diameterof the impacting face cannot be too great relative to the diameter ofthe unformed rivet shank if forming cracks and lines of weakness in theformed rivet head are to be avoided.

Still another consideration in forming eifective riveted joints withforming punch 34 is in the included angle of tapered constricting flank178. If this included angle is too small, structural iiaws in the formedhead develop with head size diameters which are sufficient to sustainrequired joint preload. On the other hand, when the included angle istoo large, the reaction force of the rivet head, being upset causes theforming punch to recoil away from the head before it is completely andeifectively formed. The reaction force problem is particularly acutewhen a forming collar or die is used because it causes constrictingilange 1106 of the FIG. 1 embodiment or constricting flange 186 of theFIG. 5 embodiment to jump olf the sheet and lose the forming collar.With the loss of forming collar constraint, the forming collars functionof preventing sheet failure from rivet expansion is lost because, at aminimum, the collar expands too much and, at the maximum, the collarfails. Moreover, even with permissible collar expansion, a longer andtherefore heavier rivet is required for an effective joint because lessrivet material is otherwise available to expand the wall of the hole inthe sheets containing the rivet.

The considerations discussed above in relation to forming punch 34 aremore particularly set forth below. With reference to FIG. 5, theincluded angle of ank 178 should be about 60. The diameter of impactingface 176 should be about 1.06 times the unformed diameter of the hardrivet shank. The diameter of bore 232 (the internal diameter of iange186) should be from about 1 to about 1.05 times the unstressed diameterof the forming collar or die. The depth of recess 174 should be about0.225 times the diameter of impacting face 176. The diameter at themouth of recess 174 should be about 1.26 times the diameter of theimpacting face.

These relationships are shown in the table below where:

nt-:included angle of flank,

al1=diameter of the impacting face,

dzzdiameter of the vmouth of the recess,

D1=unformed diameter of the rivet shank,

D2=outside diameter of the forming collar,

D3=the internal diameter of the constricting flange, and l1|=depth ofthe recess.

TABLE Item: Value oc 60 d1 I1.06D1 D@ to 1.05D2 lh d2 1.26d1 D2 1.42D1

In order to control the velocity of impacting hammer 28 as it progressesdown barrel 32 toward `forming punch or die 34, expansion chamberassembly 36 is provided. As was previously mentioned, this expansionchamber assembly allows for the control of the volume and hence thepressure of the expanding gases generated by the discharge of explosivecharge or cartridge 20.

The chamber assembly is integral with breech coupling member 112. Thechamber has a duct y188 in register with annular groove 126 and, hence,with cartridge receiving chamber 130 through radial expansion port 128.Duct 188 opens into an enlarged chamber 190. A plug 192 caps an end ofchamber 190. A piston ',194 closes the other end of the chamber.

Piston 194 is mounted on a lead screw 196 which is received in threadsat the end of a body A198 of the expansion chamber assembly. Acalibration wheel 200 engages the threads of lead screw 196 and isconstrained against axial movement with respect to body 198 by itsreceipt in a narrow slot 202 in the body. Rotation of calibration wheel200 produces longitudinal, axial movement of piston 194 which in turnproduces a greater or lesser expansion volume of chamber 190.

Piston 194 includes a sealing element 204 which may be made ofphosphorus-bronze. This sealing element is cup or dish-shaped such thatits wall, proximate the walls of chamber 190, may expand in response tothe pressure generated by explosive charge 20 and seal the low-pressureside of the chamber. A back-up or support member 206 mounts seal 204 andprovides pressure ntegrity for the seal. These elements are madeseparate in order to increase the life of the piston.

One unique safety interlock of the present invention includesphotosensitive cell or element 46 of well known construction. Housing 56is provided for receiving this photosensitive element. This housing ismounted on breech block through a mounting bracket v207. Annular lightsource 44 is disposed within sighting bore 54- of housing 56, as is thephotosensitive element. Sighting bore 54 includes an enlarged lightguide portion 208 to columnate the light emanating from source 44 into abeam for striking parabolic mirror 38 mounted on arm or mount 40 of noseassembly 14. Arm 40, and hence universally rotatable head or ball member42 of nose assembly |14, is normally maintained askew from the axis ofthe gun in order to prevent light from light source 44 from beingreflected from the parabolic mirror to the light sensitive element ofphotocell 46. When sheet abutting surface or face 50 is normal to theaxis of barrel 32, light reflected from parabolic mirror 38 will strikethe light sensitive element of photocell 46.

As illustrated in FIG. 8, photocell 46 and light source 44 are part of acircuit for controlling the element of interlock solenoid 48. Thiselement, indicated by reference numeral 210, is normally disposed in therotational path of trigger 24, as illustrated in FIGS. l and 4. A powersource, such as a DC battery 212, is in series circuit with light source44. This power source also provides the power for an amplifier 214 whichampliies the signal from photocell 46. The resultant amplified signalenergizes a coil 216 of a relay l21-8 when the circuit from the coil toground is completed. The energization of this coil closes normally opencontacts 220 of the relay to establish a circuit to the coil of solenoid48 through a current limiting resistor 222.

Thus, when photocell 46 does not generate current, because lightreilected from parabolic mirror 38 does not strike it, contacts 220 areopen and the coil of solenoid 48 is out of circuit. As a consequence,element 210 of solenoid 48 is in the path of trigger 24. However, whenlight from light source 44 vreflects off parabolic mirror 38 andphotocell 46 receives the reflected light, contacts 220 close towithdraw element 210 from the path of trigger 24 to allow the ring ofexplosive cartridge charge 201. With the exception of light source 44,photosensitive cell 46 and solenoid 48, the balance of the circuitelements 1 1 shown in FIG. 8 associated with gun alignment, may becontained in a power pack 224 in handle or grip body 146. FIG. 8 alsoillustrates additional ring interlocks which will be described withreference to FIG. 7.

FIG. 5 illustrates an alternate embodiment of the nose assembly for theimproved rivet gun of the present invention. This figure alsoillustrates to a better extent the construction of the muzzle end ofbarrel assembly 12. The modified nose assembly, indicated by referencenumeral 226, does not include the universally rotatable head previouslydescribed. The nose assembly is mounted for limited translation onreduced diameter section 90, the muzzle end of barrel assembly 12. Thenose assembly includes an annular mounting collar 228 disposed about thereduced diameter portion of barrel assembly 12. As in the previouslydescribed embodiment, an annular shoulder 230 of the nose assembly isresponsive to gas pressure within annulus 80 to urge the nose assemblyagainst a sheet when the gun is fired. Enlarged diameter section 182 ofthe noses bore permits limited longitudinal movement of forming punch34. Inwardly directed radial flange 186 serves to confine forming punch34 within bore 182 and to constrict the radial expansion of a formingcollar. This flange also defines a reduced diameter portion 2-32 of thenoses bore and a part of a sheet abutting face or surface 234 of noseassembly 226.

As in the embodiment described in FIG. 1, compression spring 96 servesto bias slightly the nose assembly towards the muzzle end of the gun andto buffer the impact of the radial shoulder, of which shoulder 230 is apart, on the end of reduced diameter section 90` of barrel housing 58(shown in FIG. 1). Gas from annulus 76 passes through passages 84 andinto annulus 80 for urging against shoulder 230. This gas also passethrough irnpacting hammer return ports 82 for the return of theimpacting hammer to the breech end of barrel 32 after the setting of arivet. O-ring 94 provides a sliding seal between mounting collar 228 andreduced diameter portion 90.

FIG. 6 illustrates an alternate form of an impacting hammer of thepresent invention which is generally indicated by reference numeral 236.The impacting hammer includes a cylindrical body portion 238 and a capportion 240. Cap portion 240 is received as by an interference fit intoa bore 242 within the body portion. The bore forms a part of a cavity244 which is partially filled with a heavy fluid-like material such asmercury, shown by reference numeral 245. The leading portion of cavity244 has a plurality of stepped, cylindrical sections 246 ofprogressively reduced diameters. These sections are joined byfrusto-conical transition shoulders 248. The cap also has a plurality ofprogressively reduced diameter, cylindrical sections 250 joined byfrusto-conical transition shoulders 252. The cylindrical sections in thecap form a part of cavity 244.

It has been found that transition sections, such as indicated at 248between the reduced diameter sections of cavity 244, act to prolong theimpact provided by impacting hammer 236 on forming punch 34 byprogressively arresting the motion of the mercury toward the muzzle endof the cavity after body 238 is decelerated by its striking of formingpunch 34. The mercury acts on the transition sections to impart a forceto the body represented by the product of the arrested mercurys mass anddeceleration. The transition sections in the cap also act to distributethe impact of the mercury over a sustained period when the impactinghammer strikes the breech plug at its return from the muzzle end of thebarrel. In this instance, the steps act to prevent too sudden an impacton the breech plug. One embodiment of the present invention which hasbeen tested on high strength titanium of this weight.

As in the case of impacting hammer 28, impacting hamrivets employs animpacting hammer weighing approximately 68 grams with the mercuryconstituting 18 grams 12 mer 236 has a reduced diameter section 254 topresent an annular shoulder 256 to gases admitted through irnpactinghammer return ports 82. An expansion ring (not shown, but similar to theone shown in FIG. l by reference numeral 173) may be used to arrestimpacting hammer 236 at the breech end of barrel 32.

FIG. 7 is directed to an alternate embodiment of the rotatable orpivotable head of the present invention and illustrates, as well,additional firing interlocks which sense the presence of a formingcollar and a bucking bar often used in riveting. Only those portions ofthe rivet gun of the present invention which are germane to theseembodiments of the invention are shown and described.

In general, the embodiment illustrated in FIG. 7 includes an innerbarrel 258 disposed for limited longitudinal movement Within a barrelhousing that includes section 260. Barrel housing section 260corresponds to second section 62 of the FIG. l embodiment. A modifiednose assembly 262 is provided which includes a nose proper defined by asleeve 264, a universally rotatable or pivotable head 266, and amounting collar 268. A modified forming punch or die 269 is disposed forlimited longitudinal movement within sleeve 264. A firing interlockcircuit 270 prevents gun firing until a bucking bar and forming die aresensed.

As in the previously described embodiment, inner barrel 258 has anannular guiding flange 271 proximate its muzzle end for maintainingalignment of the inner barrel within the barrel housing. A plurality oflongitudinally extending gas passages 272 are disposed within flange 271to allow gas to pass and bias sleeve 264 of nose assembly 262 againstthe sheets being riveted and to return the impacting hammer to itsprefiring position. To effect gas communication for this purpose, aplurality of circumferentially disposed ports 274 pass through innerbarrel 258 into a longitudinal annulus 276. Annulus 276 is defined bythe outer circumferential wall of inner barrel 258 and the inner wall ofbarrel housing section 260.

A ange 278 on inner barrel 258 is disposed proximate pressurizing ports274 towards the breech end of the gun. This flange receives an O-ring280 in sealing engagement with the inner wall of housing section 260 toeffect a gas seal between annulus 276 and the breech end of the gun.

An inner barrel return spring 282 biases inner barrel 258 towards themuzzle end of the gun by engaging ange 278 and the barrel housing. (Theengagement of return spring 282 with the barrel housing may be effectedas in the embodiment illustrated and described with reference to FIG.l.)

The muzzle end of barrel 258 is inclined at a slight angle to the normalof the longitudinal axis of the barrel as indicated by reference numeral284. This inclined or angled end of barrel 258 urges against sleeve 264to cant nose assembly 262 with respect to the axis of barrel 258 andnormally maintain the longitudinal axes of the barrel and the sleeve outof alignment. When the sleeve and the barrel are aligned, a space isdeveloped between the two. This space acts as the impacting hammerreturn port of the previously described embodiments.

A reduced diameter section 286 of barrel housing section 260 is threadedfor securely receiving a mounting collar 268. These threads areindicated by reference numeral 288. Pivotable head 266 is carried by themounting collar through mating receipt of a spherical bearing surface289 of the head in spherical seat 290 of collar 268. As in thepreviously described embodiment, the outer end of collar 268 is swedgedover spherical bearing surface 289 to retain pivotable head 266 with thecollar. In this embodiment, both collar 268 and head 266 are retainedwith barrel housing section 260 and thus are not capable of limitedlongitudinal movement with respect to the barrel housing. `It is sleeve264 which is capable of longitudinal movement and gas biasing againstthe sheets. But as before, head 266 is capable of pivotal or rotationalmovement to align the gun.

Pivotable head 266 has a sheet abutting face or surface 291 and aparabolic mirror 292. The parabolic mirror is supported by an arm 294 ofthe pivotable head. The mirror is maintained out of alignment with alight source and a photosensitive cell by the forced inclination ofsleeve 264 and the latters carried head 266 effected by the inclinationof barrel end 284. The photosensitive cell and light source areillustrated and described with reference to FIGS. 1 and 8.

Sleeve 264 receives forming punch or die 269 for limited translationalmovement therein. The sleeve has an external flange 296 which meets areduced diameter section 298. The external flange provides a stop forretaining the sleeve With the pivotable head. Return spring 282 actsthrough angled muzzle end 284 to normally maintain flange 296 againsthead 266 and to positively maintain sleeve 264 and forming punch 269 outof alignment with barrel 258. The outer muzzle end of sleeve 264 has asheet abutting surface which is defined in part by an annular, radialconstricting flange 300. The flange bounds a bore 302 for the rivet tobe upset. Flange 300 keeps forming punch 269 in sleeve 264 and retains aforming collar or die to be described. The external or extreme outer endof bore 302 is enlarged for receiving an annular indexing flange of theforming die. The inner end of sleeve 264 is larger in outside diameterthan barrel 2.58, as indicated at 304, to provide a surface for the-gasbiasing of sleeve 264 against a sheet to be riveted. The inner end ofsleeve 264 also has a retaining iiange 305 for forming punch or die 269.The retaining flange defines a bore large enough for the passage of theimpacting hammer.

IForming punch 269 is of a generally cylindrical configuration andtherefore avoids the problem of stress risers occasioned by variationsin cross-sectional area. As in the previously described forming punch,forming punch 269 has a frusto-conical recess 30-6 with an impactingface 308 at right angles to the axis of the punch. The impacting facemeets a tapered Hank 310 which diverges from the face towards the outerend of the forming punch.

lSleeve 264 is translatable within pivotable head 266, towards thebreech end of the gun from its stop position against the head, butcarries the head for pivoting within mounting collar 268.

The particular conguration of the bore of sleeve 264 allows the use of aforming die having an external indexing flange. The forming die isindicated by reference numeral 312 and its indexing ange is indicated byreference numeral 314. When properly oriented on a rivet 316, theindexing flange is towards the manufactured head of the rivet. If theforming die were inadvertently inverted it would not be received in bore302 of sleeve 264. When properly received in the bore, a circuit iscompleted to ground by the engagement of the cylindrical outer surfaceof forming die 312 with a contact 318 of circuit 270. Contact 318 andthe forming die, then, act as a switch, as shown schematically in FIG. 8by reference numeral 320.

The sensing of the presence of a bucking bar 322 on the manufacturedhead of the rivet will now be described. When forming punch 269 isplaced over the end of the rivet to be formed, it is displaced towardthe breech end of the gun. In doing so, it engages inwardly directedretaining flange 305 of sleeve 264 which in turn engages muzzle end 284of inner barrel 258. T he sleeve will then move towards the breech endby overcoming the force of inner barrel return spring 282 to allow ange278 to actuate a switch 324 of circuit 270. Switch 324 is disposed inbarrel housing section 260. As indicated in FIG. 8, the closing ofswitch 324 completes the circuit from the coil of relay 218 to ground,enabling the closing of contacts 220 and the withdrawal of element 210from the trigger 24.

The operation of the presently preferred embodiments of the presentinvention will initially be described with specific reference to lFIGS.1, 5, 6 and 8. Nose assemblies 14 14 and 226 will both be referred to inthis operational description, as well as impacting hammers 28 and 236.

An explosive charge 20 is placed in cartridge receiving chamber ofbreech plug 122 by unscrewing the barrel assembly together with breechcoupling member 112 from breech block 120. The gun is then placed overthe extending portion of a rivet 316 which extends from a pair of sheets326 and 328 to be joined. A standard bucking bar 322 is used to abut thepreformed or manufactured head of the rivet and, therefore, to maintainthe rivet Within the holes in the sheets. A forming collar or die 330 isinserted over the shank of the rivet and engaged by annular constrictingflange 186 of nose assembly 226. At this stage, the nose portion of thegun and the rivet to be driven `appear as in FIG. 5.

With particular reference to the embodiment of the invention shown inFIGS. 1 and 8, hammer 26 is cocked to bring sear 162 against the shankof the hammer and out of engagement with recess 164. The operator maymaintain finger pressure on trigger 24 but the gun will not fire untillight from light source 44 strikes parabolic mirror 38 and is reflectedtherefrom and received by photosensitive cell 46. In the embodimentillustrated in FIG. 1, this will not occur until sheet abutting face 50is normal to the axis of barrel 32 to axially align rivet 316 With thebarrels axis. Alignment is impossible until this condition occursbecause spring 110 normally keeps mirror 38 out of reflective alignmentwith photooell 46. At this point, a circuit is completed to the coil ofrelay 218 to close normally open .contacts 220 and establish a circuitto solenoid 48, circuit completion being possible in the absence ofswitches 320 and 324. With a circuit established, solenoid 48 withdrawsits element 210l from the path of trigger 24. Trigger 24 may then bedepressed to rotate about pin 156 in a clockwise direction to bring sear162 into register with recess 164, allowing hammer 26 to strike firingpin assembly 18.

When hammer 26 strikes firing pin assembly 18, tiring pin will strikethe rim of explosive charge 20) to detonate the charge. Gases from thecharge will be admitted through port 128 into duct 188 and urge againstthe rear impacting hammer 28 (or impacting hammer 236 in the case of theFIG. 6 embodiment). The volume of chamber has been present by rotatingcalibration Wheel 200 either clockwise or counterclockwise to increaseor decrease its volume. The gas -will act on the impacting hammer toaccelerate it towards the muzzle end of barrel 32 at a rapid rate. Asthe impacting hammer passes pressurizing ports 78, gas is admitted intoannulus 76 to urge against ange 72 to begin the retraction of barrel 32toward the breech end of the gun. Gas will also be admitted throughimpact hammer return ports 82 at about the time the impacting hammerstrikes forming punch or die 34.

The forming punch will then feel a sustained impact. In the instancewhere impacting hammer 236 is used, the sustained impact is occasionedby mercury 245 within the hammer continuing progressively forward andencountering frusto-conical transition shoulders 248 of body 238.Mercury 245 will eventually till that portion of the cavity bounded ordefined by stepped, cylindrical sections 246, as indicated in FIG. 6.The sustained impact effect on forming punch or die 34 will also bepresent when impacting hammer 28 is used because of the discrete actionof its cylindrical segments.

When the impacting hammer strikes forming punch 34, inward face 176 willstrike the end of the rivet and begin the upsetting process. Asupsetting proceeds, the rivet will expand radially against flank 178 ofthe forming punch while being displaced into the rounded portion offorming collar or die 330. Owing to this impact, the rivet will alsouniformly swell against the walls of the holes in the sheets in which itis inserted. A iinally formed rivet is shown in FIG. 6 at about the endof the impact from impacting hammer 236.

During the upsetting of the rivet, nose assemblies 14 and 226 will bemaintained firmly against the sheets being riveted. In the FIG. lembodiment, gases admitted through ports 78 will urge against shoulder92 to gas bias collar 88 and its carried head 42 against the sheetswhile barrel housing 58 and barrel 32 are experiencing recoil. In theFIG. 5 embodiment, gas will act against shoulder 230 to urge noseassembly 226 against the sheets during gun recoil.

At about the time that the rivets being upset or formed, the gasesadmitted through impacting hammer return ports 82 surround the reduceddiameter portion of the impacting hammer, leading segment 170 forimpacting hammer 28, and reduced diameter section 254 for impactinghammer 236, to act on the shoulder thereof and accelerate the hammertoward the breech end of barrel 32. Barrel 32 will be at the breech endowing to gas pressure acting on flange 72. With the barrel at the breechend, spent gases generated by the explosive charge -will vent throughexhaust ports 87 and discharge ports 116. After venting, inner barrelreturn spring returns barrel 32 to the muzzle end of the gun. Theimpacting hammer progresses down the barrel toward the breech end andstrikes the exposed end of breech plug 122. Expansion ring 173 preventsthe impacting hammer from bouncing toward the muzzle end of the barrelafter the impacting hammer strikes the breech plug.

The embodiment of the invention illustrated in FIG. 7 operates asfollows.

An operator places nose assembly 262 against sheet 326 with rivet 316and forming die 312 registered in bore 302 of sleeve 264. As waspreviously mentioned, the forming die can only enter bore 302 whenindexing flange 314 is against the sheet to be riveted. With sleeve 264and forming punch 269 over the end of the rivet to be formed, theforming punch pushes the sleeve and the inner barrel towards the muzzleend of the gun to close switch 324 when annular constricting flange 300yis with the sheet abutting surface of universally pivotable head 266.The operator then must orient the gun such that the axis of the bore ofbarrel 258 is coaxial with the axis of the bore of sleeve 264. Uponproper alignment, mirror 292 will be in position to reect light from alight source to a photosensitive element to release the triggerinterlock, as described with reference to FIG. l. The alingment of thebore axes of barrel 258 and sleeve 264 will develop a space between thebarrels muzzle end and the sleeve which acts to admit gas generated bythe explosive charge to pass in ahead of the impacting hammer and returnit to its prefiring position. Gas passing through passages 272 will alsourge sleeve 264 against the sheet, notwithstanding gun recoil. Relativemovement between sleeve 264 and head 266 is possible in the ringposition because external ange 296 is displaced from pivotable head 266.Thus, for gas biasing purposes of the nose against a sheet, sleeve 264replaces the mounting collars and rotatable heads of the previousembodiments in their translation capacities.

The alignment of the axes of the bores of sleeve 264 and barrel 258, theclosing of switch 324 by flange 278', and the completed circuit toground through contact 318 allow the gun to be fired in the manner ofthe FIG. 1 embodiment. Thus, tiring is only possible when an operatormanipulates the gun to align the axes of barrel 258 and sleeve 264, anoperation which assures against inadvertent gun discharge. Moreover,unless the forming collar or die and the bucking bar are sensed bycontact 318 and switch 324, respectively, ring is impossible.

In all the embodiments of the present invention, the frusto-conicalrecess in forming punches 34 and 269, and constricting anges 106, 186,300 materially add to the rivet setting ability of the rivet gun. Aspreviously described, the frusto-conical recesses constrain radialexpansion of the formed rivet head in a manner which prevents rivetfailure. The constricting ange is always in proper position because ofnose biasing and therefore forming collar failure from excessiveexpansion is overcome and the collar is always in proper position toprevent sheet failure from excessive rivet formed head expansion in thesheets.

What is claimed is:

1. An explosively actuated rivet setting gun comprising:

(a) a barrel having a breech end and a muzzle end;

(b) means for receiving an explosive charge at the breech end of thebarrel;

(c) means for closing the breech end of the barrel and for introducingan explosive charge to the explosive charge receiving means;

(d) means for selectively firing an explosive charge in the explosivecharge receiving means;

(e) an impacting hammer disposed in the barrel for translation from thebreech end toward the muzzle end in response to the tiring of anexplosive charge by the firing means;

(f) a nose mounted on the gun for limited longitudinal movement at themuzzle end of the barrel, the nose including a sheet abutting surfacefor abutting against the exposed side of a sheet through which an end ofa rivet to be set extends and a bore for receiving the end of the rivet;

(g) means responsive to gas pressure generated by the detonation of theexplosive charge to urge the nose against the sheet during recoil of thesetting gun; and

(h) a forming die at the muzzle end of the barrel disposed to be struckby the impacting hammer and in turn to strike the end of a rivetextending into the bore of the nose.

2. The rivet setting gun claimed in claim 1 wherein the forming die hasa frusto-conical recess dening an impacting face normal to the axis ofthe forming die for striking an end of a rivet to be upset and a taperedi'lank converging from the impacting face to the muzzle end of theforming die to conne radial expansion of the rivet to be upset.

3. The rivet setting gun claimed in claim 2 wherein:

(a) the nose includes an annular, radial ange extending inwardly towardthe axis of the noses bore from the sheet abutting surface forconstricting the radial expansion of a forming collar utilized with therivet, the radial flange defining a reduced diameter portion of thenoses bore; and

(b) the forming die is disposed longitudinally inward of the radialflange for limited longitudinal movement in the noses bore.

4. The rivet setting gun claimed in claim 3 wherein:

(a) an outer barrel housing is provided, the Outer barrel housingencasing the barrel; and

(b) the nose urging means includes at least one pressurizing port in thebarrel, the pressurizing port being in pressure and gas communicationwith the nose between the barrel housing and the barrel to urge the noseagainst the sheet.

t5. The rivet setting gun claimed in claim 4 wherein the impactinghammer includes at least two inertia portions coupled together such thatupon acceleration from the breech end toward the muzzle end of thebarrel one of the portions will lag behind the other and upon strikingthe forming die a sustained impact will be delivered to the forming die.

6. The rivet setting gun claimed in claim 5 wherein the impacting hammerinertia portions comprise a plurality of segments longitudinally coupledtogether.

7. The rivet setting gun claimed in claim 5 wherein the impacting hammerinertia portions comprise:

(a) a body having a longitudinal cavity of progressively reducedtransverse cross sectional area toward the muzzle end of the impactinghammer; and

(b) a heavy fluid-like material partially lling the cavity.

8. The rivet setting gun claimed in claim 5 including an expansionchamber assembly having an expansion v 17 chamber, means for adjustingthe volume of the expansion chamber, and means for communicating theexpansion chamber with the gases generated by the detonation of theexplosive charge between the breech end of the barrel and the explosivecharge receiving means.

9. The rivet setting gun claimed in claim 8 wherein:

(a) a universally rotatable head is disposed on the muzzle end of thegun, the noses bore extending through the head and being rotatabletherewith; and

(b) means is provided for preventing tiring of the gun until the nosesbore is coaxial with the axis of the barrel.

10. The rivet setting gun claimed in claim 1 including:

`(a) an outer barrel housing encasing the barrel, the

barrel being disposed for limited longitudinal movement in the barrelhousing between a rst and a second position, the rst position beingtoward the nose and the second position being away from the nose;

(b) biasing means for urging the barrel toward its r-st position; and

(c) the nose urging means includes at least one pressurizing portassociated with the barrel and the nose to urge the nose against thesheet with expanding combustion gases from the explosive charge afterthe impacting hammer reaches a predetermined point in the barrel.

11. The rivet setting gun claimed in claim 10 wherein the nose urgingmeans includes an annulus between the outer barrel housing and thebarrel in pressure communication with the port and a surface of the nosesuch that gases produced by the ring of the explosive charge act againstthe surface to urge the nose against the sheet.

12. The setting tool claimed in claim 11 including at least oneimpacting hammer return port at the muzzle end of the barrel incommunication with the annulus for admitting gases generated by theexplosive charge into the barrel to return the impacting hammer to thebreech end of the barrel.

13. The rivet setting gun claimed in claim 12 including:

(a) at least one gas exhaust port at the breech end of the barrel whichis normally closed by the barrel housing; and

(b) at least one gas discharge port disposed in the gun forcommunication with the exhaust port when the barrel is in its secondposition and to vent gases generated by the explosive charge toatmosphere.

14. An explosively actuated tool for setting a rivet fabricated fromhard material comprising:

(a) a barrel assembly having a barrel housing, a barrel, a muzzle endand breech end, the barrel being mounted in the barrel housing forlimited longitudinal movement therein, a barrel return spring disposedto act between the barrel housing and the barrel to urge the barrel inthe direction of the muzzle end, at least one pressurizing port throughthe wall of the barrel intermediate the ends of the barrel, meansoutside the barrel to pressure communicate the pressurizing port withthe muzzle end of the barrel assembly, at least one impacting hammerreturn port at the muzzle end of the barrel communicating the bore ofthe barrel with the pressure communication means, and means to vent thebarrel of explosive generated gases when the barrel moves towards thebreech end;

(b) a nose mounted at the muzzle end of the barrel assembly forlongitudinal translation thereon, the nose having a surface in pressurecommunication with the pressure communication means such that uponsensing of a pressure generated by the gases formed in the ring of anexplosive charge the barrel moves longitudinally away from the nose, anda bore for receiving an end of a rivet extending from the sheet;

(c) a breech block assembly normally closing the breech end of thebarrel assembly and attached to the barrel housing, ythe breech blockassembly having means for receiving an explosive charge and means forintroducing an explosive charge to the receiving means;

(d) means for igniting an explosive charge received in the receivingmeans;

(e) a forming die disposed for longitudinal translation in the nosesbore, the forming die having a frustoconical recess converging towardthe exposed end of the forming die and an impacting face normal to theaxis of the forming die for respectively constraining the expansion ofthe end of a rivet to be upset by the tool and striking such rivet end;and

(f) an impacting hammer disposed for translation in the bore of thebarrel between the breech end and the muzzle end, the impacting hammerhaving at least two inertial masses coupled together such that uponstriking the forming die at the muzzle end a sustained impact isimparted thereto, the impacting hammer being capable of returning to thebreech end after striking the forming die by pressure generated by thegases formed in the tiring of an explosive charge admitted through theimpacting hammer return port.

15. The explosively actuated tool claimed in claim 14 wherein theimpacting hammer includes:

(a) a body portion having an axial cavity which progressively reduces intransverse cross-sectional area toward the muzzle end thereof; and

(b) a heavy fluid-like material partially iilling the axial cavity.

16. The explosively actuated tool claimed in claim 15 wherein the breechend of the cavity has a cross-sectional area which progressively reducestoward the breech end.

17. The explosively actuated tool claimed in claim 15 wherein theprogressively reducing transverse cross-sec tional area at the muzzleend of the impacting hammer is defined by a series of progressivelyreduced diameter cylindrical sections.

18. The explosively actuated tool claimed in claim 17 wherein:

(a) the progressively reduced diameter cylindrical sections are joinedby frusto-conical transition shoulders;

(b) the body portion has a reduced diameter section at the muzzle end ofthe impacting hammer to present an impacting hammer return surface atthe juncture of the reduced diameter section and the balance of theimpacting hammer; andy (c) means is provided to compressively engage theWall of the barrels bore to retain the impacting hammer at the breechend of the barrel upon return from the muzzle end thereof.

19. The explosively actuated tool claimed in claim 18 wherein:

(a) the breech end of the cavity has a series of progressively reduceddiameter cylindrical sections joined together by frusto-conicaltransition shoulders; and

(b) the heavy fluid-like material is mercury.

20. The explosively actuated tool claimed in claim 14 wherein theimpacting hammer is dened by a plurality of cylindrical segmentslongitudinally coupled together such that upon acceleration toward themuzzle end progressive segments toward the breech end lag behindsegments toward the muzzle end.

21. The explosively actuated tool claimed in claim 20 wherein thecylindrical segments are coupled together through a longitudinal pinwhich exerts a radial, outwardly directed force on the walls of thebores in the segments in which the pin is disposed.

22. The explosively actuated tool claimed in claim 21 including:

(a) means to compressively engage the wall of the barrels bore to arrestthe impacting hammer at the breech end of the barrel upon return fromthe muzzle end thereof; and

(b) the segment at the muzzle end of the impacting hammer has a reduceddiameter to present a surface for gas from the impacting hammer returnport to act upon.

23. The rivet setting tool claimed in claim 14 wherein:

(a) the nose assembly includes a universally pivotable head mounted atits end, the sheet abutting surface being on the universally pivotablehead; and

(b) aligning means is provided including:

(i) a parabolic mirror mounted on the universally pivotable head;

(ii) a source of light for directing a beam of light at the parabolicmirror;

(iii) a photosensitive cell disposed to be energized by light reflectedfrom the parabolic mirror; and

(iv) means to prevent the actuation for the firing means until thephotosensitive cell generates a tiring signal in response to light fromthe light source being reflected from the parabolic mirror.

24. The rivet setting tool claimed in claim 23 including: biasing meansurging against the universally pivotable head to normally position theparabolic mirror such that light from the light source reected from theparabolic mirror will not strike the photo sensitive cell until the boreof the nose assembly is coaxial with the bore of the barrel.

25. The rivet setting tool claimed in claim 24 including a housingmounted on the tool having a bore, the photosensitive cell and the lightsource being mounted in the bore such that light emanating from thelight source is directed as a beam toward the muzzle end of the `barrelassembly.

26. The rivet setting tool claimed in claim 25 wherein:

(a) the firing means includes a trigger; and

(b) the firing prevention means includes a solenoid in circuit with thephotosensitive cell having an element responsive to the energization ofthe solenoids coil, the solenoid being mounted such that its element isin the path of the trigger until the solenoids coil is energized.

27. The rivet setting tool claimed in claim 14 wherein:

(a) the nose includes a universally pivotable head mounted to the barrelassembly at such assemblys muzzle end, the bore of the nose being in thepivotable head;

(b) means is provided to normally maintain the bore of the nose out ofaxial alignment with the bore of the barrel; and

(c) means is provided to prevent actuation of the ring means until thebore of the nose is coaxially aligned with the bore of the barrel.

28. The rivet setting tool claimed in claim 27 wherein the means tomaintain the bore of the nose out of axial alignment with the bore ofthe barrel includes:

the muzzle end of the barrel and an inner end of the nose being normallyin abutting relationship with the abutting surfaces such that the boreof the nose is out of alignment with the bore of the barrel until thetool is aligned by pivoting the nose with the pivotable head, withrespect to the barrel.

29. The rivet setting tool claimed in claim 28 wherein the nose includesa sleeve having the noses bore, the forming punch being slidablydisposed within the sleeve, and the inner end of the nose in normalabutting relationship with the muzzle end of the barrel is on thesleeve.

30. The rivet setting tool claimed in claim 29 wherein the sleeve isslidable in the pivotable head and has an outer end extending beyond asheet abutting surface thereof such that sucient compressive engagementof the sleeve on a sheet causes the outer end of the sleeve to becomeflush with the sheet abutting surface by displacing the barrel andbarrel return spring towards the breech end of the tool.

31. The rivet setting tool claimed in claim 30 wherein:

the nose includes a mounting collar xedly secured to the barrel housingand rotatably receiving the pivotable head;

the sleeve displaces the barrel against the return spring to maintainthe bore of the sleeve normally out of alignment with the bore of thebarrel.

32. The rivet setting tool claimed in claim 31 including:

means for preventing the actuation of the ring means until the sensingof the correct position of a bucking bar; and

means for preventing the actuation of the ring means until the sensingof the correct position of a forming collar used with the rivet.

33. The rivet setting tool claimed in claim 32 wherein the means toprevent actuation of the firing means until the bore of the pivotablehead is coaxially aligned with the bore of the lbarrel includes:

(a) a parabolic mirror mounted on the pivotable head;

(b) a source of light for directing a beam of light at the parabolicmirror;

(c) a photosensitive cell disposed to be energized by light reflectedfrom the parabolic mirror; and

(d) means to prevent actuation of the ring means until thephotosensitive cell generates a firing signal in response to light fromthe light source being reflected from the parabolic mirror.

34. An explosively actuated rivet setting gun compris- (a) a barrelassembly having a barrel with a muzzle end and a breech end, apressurizing port intermediate the ends of the barrel, and means incommunication with the pressurizing port for communicating thepressurizing port with the muzzle end of the barrel;

(b) a nose mounted to the barrel assembly at the muzzle end for limitedlongitudinal translation thereon, the nose assembly having a pressuresurface in pressure communication with the pressurizing port through thecommunicating means such that upon the presence of a pressure generatedby the gases formed in the firing of an explosive charge the noseassembly is urged away from the barrel assembly, a flat sheet abuttingsurface for abutting against the sheet of material to be riveted, yand abore for receiving an end of a rivet extending from the sheet;

(c) means for receiving an explosive charge at the breech end of therbarrel;

(d) means for closing the breech end of the barrel and for introducingan explosive charge to the explosive charge receiving means;

(e) means for selectively firing an explosive charge in the explosivecharge receiving means;

(f) an impacting hammer disposed in the barrel for translation from thebreech end toward the muzzle end in response to the ring of an expolsivecharge by the firing means; and

(g) a forming die at the muzzle end of the barrel disposed to be struckby the impacting hammer and in turn to strike the end of a rivetextending into the bore of the nose.

35. The explosively actuated rivet setting gun claimed in claim 34wherein the nose includes an annular mounting collar slidably disposedabout the barrel assembly at the muzzle end thereof and in gastightrelationship therewith.

36. The explosively actuated rivet setting gun claimed in claim 35wherein the barrel assembly includes a barrel housing which receives thebarrel and the communicating means includes an annulus betwen the barrelhousing and the barrel in pressure Comunication with the pressurizingport and the noses pressure surface.

37. The explosively actuated rivet setting gun claimed in claim 36wherein:

(a) the nose is received for limited longitudinal movement on thebarrel; and

(b) at least one impacting hammer return port is provide at the muzzleend of the barrel in pressure and gas communication with the annulus.

38. An explosively actuated rivet setting gun comprismg:

(a) a barrel having a breech end and a muzzle end;

(b) means for receiving an explosive charge at the breech end of thebarrel;

(c) means for closing the breech end of the barrel and for introducingan exposive charge to the charge receiving means;

(d) means for ring an explosive charge in the explosive charge receivingmeans;

(e) an impacting hammer disposed in the barrel for translation from thebreech end toward the muzzle end in response to the firing 0f anexposive charge by the firing means;

(f) a forming die at the muzzle end of the barrel disposed to ibe struckby the impacting hammer, the forming die having a frusto-conical recessdefining an impacting face normal to the laxis of the forming die forstriking the end of a rivet t0 be upset and a tapered flank convergingfrom the impacting face to the muzzle end of the forming die to confineradial expansion of the rivet to be upset; and

(g) means to retain the forming die with the gun.

39. The explosively actuated rivet setting gun claimed in claim 38wherein the included angle of the forming die ank is about 60.

40. The explosively actuated rivet setting gun claimed in claim 39wherein the depth of the forming die recess is about 0.225 times thediameter of the impacting face.

41. The explosively actuated rivet setting gun claimed in claim 40wherein the diamteer of the impacting face of the forming die is about1.06 times the unformed diameter of the shank of the rivet to be upset.

42. The explosively actuated rivet setting gun claimed in claim 41wherein the means for retaining the forming die with the gun includes anannular radial constricting flange at the muzzle end of the gun, theconstricting flange defining a bore for the passage of the shank of arivet to be upset and for constricting the radial expansion of a formingcollar used with such rivet, the diameter of such bore -being about 1 to1.05 times the diameter of the forming collar.

43. The rivet setting gun claimed in claim 40 wherein the impactinghammer comprises a plurality of tandemly aligned cylindrical segmentsand means for coupling the segments together such that upon striking'theforming die each of the segments acts relatively independent of theother segments to effect a sustained impact on the forming die.

44. The rivet setting gun claimed in claim 43 wherein the segments areattached together through a longitudinally disposed split retention pinreceived in holes in the segments.

45. The rivet setting tool claimed in claim 40 wherein the impactinghammer has an axial cavity, is partially lled with a heavy fluid-likematerial and the muzzle end of the axial cavity converges incross-sectional area toward the muzzle end.

46. The rivet setting gun claimed in claim 45 wherein the convergingportion of the axial cavity of the impacting hammer is defined by aseries of cylindrical sections of progressively reduced diameters.

47. The riveting gun claimed in claim 46 wherein the heavy fluid-likematerial is mercury.

48. An improved explosively actuated rivet setting tool comprising:

(a) a `barrel having a breech end and a muzzle end;

(b) an impacting hammer disposed for movement between the breech end andthe muzzle end of the barrel;

(c) a forming die disposed `at the muzzle end of the barrel for strikinga rivet upon being impacted by the impacting hammer;

(d) means for receiving an explosive charge at the breech end of thebarrel;

(e) breech means at the breech end of the barrel for closing such end ofthe barrel, the breech means being operable in the loading of anexplosive charge into the receiving means;

(f) means for firing an explosive charge received in the receivingmeans; and

(g) means for adjusting the expansion volume between the impactinghammer and the receiving means to vary the velocity of the impactinghammer.

49. The improvement claimed in claim 48 wherein the expansion volumeadjusting means includes a chamber in gas communication with theexplosive charge receiving means and an adjustable element disposed inthe chamber for varying the volume of the chamber.

50. The improvement claimed in claim 49 wherein the adjustable elementincludes a cup-shaped metal seal, the walls of the cup-shaped seal beingdeformable against the walls of the chamber in response to the pressuregenerated by the firing of the explosive charge.

51. The improvement claimed in claim 50 wherein the adjusting elementincludes a support member attached to the metal seal on the latters lowpressure side.

References Cited UNITED STATES PATENTS 3,050,732 8/1962 Termet 227-103,239,121 3/1966 Kopf 227-10 3,248,032 4/1966 Bochrnan 227-8 3,275,2099/ 1966 Hansen 227-10 3,341,101 9/ 1967 Butler 227-10 JOHN F. CAMPBELL,Primary Examiner GENE P. CROSBY, Assistant Examiner IU.S. Cl. X.R.

P04050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pltevnt N03,559,449 Dated February 2 1971 A Inventor(s) John C. ASteinmetz i It iscertifiea that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the specification: Column 5, line 32 "KJ" should l -2+. Column 7 line60 "piston" should be pistol Column 8, line 1, "gear" should be -sear.Column ll, line 34', Hpasse" 'should b e --passes. Column ll, line 71.after "titanium" insert r--riv'ets employs an impacting hamme weighingapproximately 68 grams with the mercury constitutl' 18' grams". Column11,4 lines 74 and 75 -delete "rivets employs an impactinghammer weighingapproximately 68 grams with the mercury constituting 18 grams,

Signed-rand sealed this 2nd day of November l 971 (SEAT-ly Attest:

EDWARD M.FLETCHER',JR. ROBERT GOTTSCHALK Attestng Officer ActingCommissionerof Patent.

